With the color-redshift relations of SDSS-UKIDSS-WISE quasars, we can obtain
the photometric redshifts with different sets of photometric data using the
techniques described in Section 3, and compare
the photometric redshift reliability obtained with the different photometric
data. In Figure 9, we show the comparisons of photometric redshifts with
spectroscopic redshifts
and the distributions of the differences between them for the cases
using the SDSS, SDSS+UKIDSS, UKIDSS+WISE W1,W2, and SDSS+UKIDSS+WISE W1,W2 photometric data, respectively. The photometric redshift reliability, defined as the
fraction of the sources with the difference between the photometric and spectroscopic redshifts smaller than
0.2, is 70.4%, 84.8%, 67.4% and 87.0% respectively for the above four cases. Therefore, by using the SDSS \(ugriz,\)  UKIDSS YJHK and WISE W1 and W2 band
photometric data, we can efficiently
improve the photometric redshift reliability up to 87.0%, which is significantly higher than using the SDSS
photometric data alone (70.4%). Moreover, as mentioned in Section 4 and in [1]}, using the SDSS,
UKIDSS and WISE photometric data can also help us select quasar candidates more efficiently. However,
we noticed that this can be done only in the UKIDSS surveyed area, which is much smaller than the sky
coverage of both SDSS and WISE surveys.
